(1) Field of the Invention
The present invention relates generally to a spark timing control system for an automotive vehicle, and particularly to a system which controls the spark timing of an ignition plug provided within each combustion chamber of an internal combustion engine in order to reduce the shock due to the abrupt engine braking which occurs when fuel supply cutoff is executed during deceleration from a predetermined engine speed characteristic.
(2) Background of the Invention
In conventional fuel supply control system for an internal combustion engines for vehicles (e.g., fuel injection system, carburetor, etc.), there may be provided a function by which fuel supply cutoff is executed during a specific deceleration of the vehicle in order to improve exhaust gas purification and to save on fuel consumption.
Fuel supply cutoff may be executed during deceleration of the vehicle depending upon whether particular engine operating conditions are satisfied; e.g., whether the throttle valve in the intake manifold is in the idling position, the engine rotational speed is above a predetermined value with respect to the current cooling water temperature, etc. Although in the above-described control system the fuel supply may be repeatedly cut off and resumed depending upon the operating conditions of the vehicle, cutting off or resuming the fuel supply causes a abrupt change in the driving torque of the engine.
Consequently, the vehicle occupants are often subjected to an uncomfortable shock or jolt. For example, when fuel cutoff is executed immediately after deceleration has started, a violent shock results since abrupt engine braking is applied.
Therefore, means have been proposed for delaying the time of the fuel supply cutoff for a predetermined period of time or for a predetermined number of engine rotations. However, the fuel supply control system including the delay means described above is mounted on the engine, and the driving torque of the engine still abruptly dropped to zero when the fuel supply is cut off so that an uncomfortable shock is generated even in this state.